This invention relates to a rolling machine (rolling mill) and a rolling method for rolling a sheet (strip), and more particularly to a rolling machine and a rolling method which can secure a strip crown and shape control capability for various strips from a narrow-width strip to a large-width strip.
In the sheet-rolling field, it is always required to enhance the quality of strips, and various studies and developments have heretofore been made in order to enhance the dimensional accuracy of strips. Particularly, the quality of the strip is influenced directly by the quality of the strip crown and shape of the strip, and therefore various types of rolling machines have heretofore been proposed for the purpose of enhancing the control capability for the strip crown and shape.
For example, in a four-stage rolling machine, working roll bending devices for imparting a bending force to working rolls were used in the past as means for controlling the strip crown and shape. With this method, however, the strip crown and shape could not be adequately controlled for various kinds of strip materials according to the need for various thicknesses and widths of the strip.
Therefore, rolling machines, having a higher strip crown and shape control capability, have thereafter been proposed and put into practical use.
One such example is a six-stage rolling machine comprising a pair of upper and lower working rolls, axially-movable intermediate rolls supporting these working rolls, respectively, and reinforcing rolls supporting these intermediate rolls, respectively. Another example is such a six-stage rolling machine in which each of the intermediate rolls has a S-shaped initial crown.
In these six-stage rolling machines, although the strip crown and shape control capability was considerably improved, it was difficult to secure the satisfactory strip crown and shape control capability for strips of various widths from a narrow-width to a large-width. More specifically, in the former six-stage rolling machine, the strip crown and shape control capability was not adequate for large-width strips, and in the latter six-stage rolling machine with the intermediate rolls each having the special initial crown, the strip crown and shape control capability for narrow-width strips was not adequate.
In both of the above six-stage rolling machines, the compressing position difference (leveling difference) between the operating side and the drive side was liable to occur because of the axial movement of the intermediate rolls, and considerable time and labor were required for adjusting it, and this tendency was conspicuous particularly with the latter six-stage rolling machine with the special initial crown.
In the recent continuous cold and hot rolling, it has often been required to greatly change the strip crown and shape instantaneously during the rolling operation. However, with the control depending on the axial movement, the speed of movement is limited, which has resulted in a problem that the satisfactory control response can not be obtained.
On the other hand, there have been proposed rolling machines which achieve a higher strip crown and shape control capability than the conventional four-stage rolling machines without the need for axial movement of the intermediate rolls as in the above six-stage rolling machines, and with this construction, the above problem, related to the leveling difference between the operating side and the drive side, and the above control response problem were overcome. Example of such rolling machines include a six-stage/five-stage rolling machine as disclosed in JP-A-53-66849 (U.S. Pat. No. 4,194,382) in which the axial length (barrel length) of reinforcing rolls is smaller than that of working rolls and intermediate rolls, and intermediate roll bending devices are provided, and a six-stage/five-stage rolling machine of the intermediate roll cross-type as disclosed in JP-A-61-279305, JP-A-55-36062 and U.S. Pat. No. 5,839,313 in which intermediate rolls are disposed in a crossed manner.
However, these rolling machines still have a problem that it is difficult to secure the strip crown and shape control capability for strips of various widths from a narrow width to a large width.
More specifically, in the former rolling machine with the short-barrel reinforcing rolls, a drawback of the bending that its effect becomes smaller toward the central portion of the strip is covered by the short-barrel design of the reinforcing rolls, and as a result, opposite side edge portions of a large-width strip are disposed outwardly of the opposite ends of the reinforcing rolls, and the resultant shape is such that a large concave crown is formed, and the central portion of the strip is excessively extended, thus failing to provide the desired strip crown and shape. If the barrel length of the reinforcing rolls is increased in order to overcome this difficulty, the strip crown and shape control capability for narrow-width strips is inadequate.
In the latter rolling machine of the intermediate roll cross-type, the intermediate rolls are crossed, so that a gap is formed between each intermediate roll and the associated working roll so as to provide an apparent roll crown, thereby controlling the strip crown and shape. The gap, produced at this time, is increasing toward the opposite side edges of the strip, and is decreasing toward the central portion of the strip. Therefore, the adequate strip crown and shape control capability is obtained for a large-width strip, but can not be obtained for a narrow-width strip.
As described above, in the rolling machine with the short-barrel reinforcing rolls and the rolling machine of the intermediate roll cross-type, although the strip crown and shape control capability, higher than that of the conventional four-stage rolling machines, could be achieved without suffering from the problem concerning the leveling difference between the operating side and the drive side, and the control response problem, it was difficult to secure the satisfactory strip crown and shape control capability for strips of various widths from a narrow width to a large width.
As described above, the six-stage/five-stage rolling machine with the short-barrel reinforcing rolls is advantageous in the improvement of the strip crown and shape control capability for a narrow-width strip while the six-stage/five-stage rolling machine of the intermediate roll cross-type is advantageous in the improvement of the strip crown and shape control capability for a large-width strip. Therefore, it may be proposed to secure the satisfactory strip crown and shape control capability for strips of various widths from a narrow width to a large width by combining the two rolling machines together. In this case, however, when comparing the range of the control for a narrow-width strip with the range of the control for a large-width strip, the former is inevitably extremely smaller than the latter, and this is not the essential improvement of the strip crown and shape control capability for narrow-width strips.